Antiknock motor fuels



United States 3,088,813 ANTIKNOCK MOTOR FUELS Charles A. Sandy and James H. Werntz, Wilmington,

Del., assignors to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware No Drawing. Filed July 8, 1959, Ser. No. $25,679 16 Claims. (Cl. 44-69) This invention relates to antiknock motor fuels and more particularly to motor fuels for internal combustion engines equipped with fuel injection systems which motor fuels comprise hydrocarbons in the gasoline boiling range that contain lithium salts of certain substituted carboxylic acids as antiknock agents.

It is recognized thatinternal combustion-engines knock under a widevariety of engine operating conditions, including varying speeds, degree of spark advance, compression ration, fuel/ air mixture ratio, temperatures, and intake manifold pressure. Because of these variations in engine conditions, the engine may knock under mild or severe stress. Industry recognizes that mil stress is usually encountered when the engine knocks under conditions of relatively low speed, retarded spark or low operating temperatures, such as in normally experienced in the operation of the existing type passenger car. On the other hand, severe stress is encountered under conditions of high engine speeds, advanced spark, high operating temperatures or high manifold pressures, such as are encountered with high speed operation of automotive type engines or the normal operation of aviation engines.

The development of internal combustion engines of high compression ratios has established a need for high quality fuels having increased resistance to knock over the above-mentioned wide range of engine operating conditions. Careful refining and blending of fuel components can produce a fuel of sufficiently increased knock resistance to satisfy the engine requirements under the previously mentioned conditions, but such fuels are difficult and costly to produce. Usually, tetraethyllead is today employed in these fuel blends to provide the knock resistance which cannot easily and economically be obtained through refining techniques. Tetraethyllead is widely usedsince it does impart improved antiknock quality over the wide range of engine conditions mentioned above. The use of tetraethyllead, however, has limitations. Each successive increment of tetraethyllead produces only a fraction of the improvement in antiknock rating obtained with each previous increment.

Heretofore it has been proposed to employ in motor fuels for various purposes a variety of organometallic compounds, including some organic lithium compounds (other than those of the present invention). For example, Taveau in US. Patent 1,991,127 has proposed to employ lithium alkyls and lithium aryls in motor fuels of low antiknock value. However, such lithium compounds are quite unstable and tend to decompose in the presence of moisture, air or gases such as carbon dioxide, and further-( more have little or no appreciable antiknock effect when employed in engines of thecharacter to which this invention relates. At an even earlier date, it was proposed to employ lithium oleate and lithium naphthenate as antiknock agents in straight run. gasolines having an octane number of a low order (about 50). However, lithium oleate has but little antiknock effect with the more modern motor fuels of high octane value, particularly in engines of the character to which this invention relates. Lithium naphthenate has but little antiknock effect in motor fuels of low octane value, including many of the present day motor fuels, and has a considerable antiknock effect only in highly branched aviation gasolines having a high initial octane numer and in isooctane. Other or- 3,688,813 Patented May 7, 1963- ganic metal compounds, including some lithium compounds, have been proposed for use in anti-preignition compounds that require a deposit on the piston top and, cylinder head in order to so function, and are not antiknock agents.

Itis anobject of the present invention to provide motor fuels containing new and improved antiknock compounds which are adapted for injection through the fuel injection systems of internal combustion engines which are equipped with fuel injection systems. Another object is to provide motor fuels of such character which function over the entire range of engine operating conditions. A further object is to provide new :and improved antiknock compounds for fuels which contain tetraethyllead, which new antiknock compounds increase the knock resistance of the fuel to an extent which is not attainable by the use of tetraethyllead alone. A still further object is to provide novel antiknock compounds which are superior to tetraethyllead under severe operating conditions such as are normally encountered in aircraft or in high compression automotive engines. Other objects are to provide new compositions of matter and to advance the art. Still other objects will appear hereinafter.

The above and other objects may be accomplished in accordance with the present invention wherein there is provided a motor fuel for internal combustion engines equipped with fuel injection systems which fuel comprises hydrocarbons boiling in the gasoline boiling range containing, in an amount sufficient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of the formula Li0OCQ--COOR wherein R is -a hydrocarbon radical of 1 to 18 carbon atoms of the group consisting of alkyl and alkenyl radicals and Q is a hydrocarbon radical of l to 10 carbon atoms of the group consisting of saturated acyclic, alicyclic and methylene substituted alicyclic radicals. A particular feature of this invention involves the provision of motor fuels of the above character which, in addition to the lithium compounds, contain tetraethyllead.

It has been found that the lithium compounds of this invention are very effective to increase the antiknock properties of motor fuels of varying types in the absence and in the presence of tetraet hyllead. They are effective over the entire range of engine operating conditions. In the presence of tetnaethyllead, they increase the antiknock properties of the fuel to a much greater extent than can be obtained by corresponding increases in the amount of tetraethyl-lead.

The fuels of the present invention are applicable for use in engines equipped with fuel injection systems, since with ordinary carburetion many of the antiknock compounds of this invention are not sufficiently inductable to avoid deposition in the intake system over an extended period of operation. Some of the compounds of this invention, e.g. lithium alkenyl (C C dimethylsuccinate and lithium alkenyl (C C tetramethylsuccinate, are carburetable with gasoline but, when so introduced into the engine, fail to vaporize sufficiently to exert the desired antiknock effect. While they are normally injected with the fuel itself, they may 'be injected separately as a dust or powder, or with solvents used either to carry them alone or in the supplementary antiknock solutions such as the water/alcohol mixtures employed in aircraft engines or tetraethyllead/ alcohol mixtures employed in automotive engines. These compounds are effective irrespective of Which of the above methods is used to introduce them into the cylinder of the engine.

The present invention is particularly applicable to hydrocarbon fuels for internal combustion engines and more particularly to fuels which may be a mixture of hydrocarbons boiling in the gasoline range, or a refined gasoline as defined in the ASTM D-288-53 (adopted 1939, revised 1953). Such fuels may be clear fuels or fuels containing organo-lead antiknock compounds such as tetraethyllead. Such organo-lead compounds may be used in amounts up to the equivalent of 6 ml. of tetraethyllead per gallon of fuel. When used, the organolead compound usually will be tetraethyllead and usually will be present in an amount of from about 1.5 to about 3 ml. per gallon of fuel. Also, the fuels may be finished fuels which contain varying amounts of conventional fuel additives such as scavenging agents, dyes, antioxidants, anti-icing agents, rust inhibitors, corrosion inhibitors, inhibitors of haze formation, inhibitors of gum formation, anti-preignition agents, and the like.

The lithium compounds which are employed in accordance with this invention are the lithium salts having the formula LiOOC-Q-COOR wherein R is a hydrocarbon radical of 1 to 18 carbon atoms of the group consisting of alkyl and alkenyl radicals and Q is a hydrocarbon radical of l to 18 carbon atoms of the group consisting of saturated acyclic, alicyclic and methylene substituted alicyclic radicals. It will be understood that an alkenyl radical means the radical of an olefin; an acyclic radical is an open-chain radical; and an alicyclic radical means a saturated cyclic hydrocarbon radical. A preferred class of compounds are the monoalkyl esters of the unsubstituted saturated aliphatic dicarboxylic acids which may be acyclic or alicyclic. Particularly preferred compounds are the salts of the esters of tetramethylsuccinic acid, especially the alkyl esters, e.g. lithium ethyl tetramethylsuccinate. Representative lithium salts of this invention are lithium methyl adipate, lithium isobutyl 3- rnethylene-1,2-eyclobutanedicarboxylate, lithium 2-ethylhexyl 3-methyl-1,Z-cyclobutanedicarboxylate, lithium ethyl 2,2-dimethylsuccinate, lithium ethyl tetramethylsuccinate, lithium butyl tetramethylsuccinate, lithium alkyl (C -C13) tetramethylsuccinate, lithium Z-ethylhexyl ca-mphorate, lithium ethyl dimethylmalonate, lithium ethyl isopropylmalonate, lithium ethyl isopropylsuccinate, lithium dodecyl tetramethylsuccinate, lithium alkenyl (C C tetramethylsuccinate, lithium ethyl 2,2-dimethylglutarate, and lithium ethyl pimelate. The lithium a-lkenyl (C -C tetramethylsuccinate is a mixture of the lithium salts of the mixtures of esters obtained by esterifying tetramethyl succinic acid with the alcohols present in a technical grade of oleyl alcohol rich in cetyl alcohol and unsaturated alcohols of 16 carbon atoms, usually containing about 23.5% of saturated alcohols and about 76.5% of unsaturated alcohols, the chain length being mainly of 16 and 18 carbon atoms with minor amounts of alcohols containing 14, 20, and 22 carbon atoms. Similarly, lithium alkyl (C C tetramethylsuccinate is a mixture derived from a mixture of saturated alcohols composed mainly of alcohols having a chain length of from 8 to 13 carbon atoms.

The lithium salts of this invention are readily prepared by the reaction of the appropriate monoester of the dicarboxylic acid or its anhydride with a lithium base, preferably lithium hydroxide monohydrate. Also, lithium metal, lithium hydride, lithium alkoxide or lithium carbonate may be used to advantage to form the lithium salt. The salts are readily obtained by refluxing the ester with an equal volume of water containing the stoichiometric amount of the lithium base followed by recovery of the salt from the solution. Advantageously, they are prepared by adding the stoichiometric amount of lithium metal to a solution of the anhydride of the ester in an anhydrous alcohol.

In general, the dicarboxylic acids, their esters, and their anhydrides, and the methods of preparing them are known to those skilled in the art. The monoesters of the cyclobutane-1,2-dicarboxylic acids and their salts are new compounds, but such compounds per se and the methods of preparing them form no part of this invention. The preparation of such compounds, however, are illustrated by the following Examples A and B.

Example A Part 1.-A mixture of 98.1 parts of maleic anhydride, 20.0 parts of allene, 176 parts of benzene, and 0.5 part of hydroquinone was heated in a stainless steel vessel at 225 C. for eight hours at autogenous pressure. The reactor was then cooled, opened, and the reaction mixture filtered to separate 26.2 parts of yellow solid from the liquid portion of the mixture. The unreacted benzene and maleic anhydride were removed from the filtrate by distillation. Distillation of the resultant residue afforded 21.3 parts of 3-methylene-1,2-cyclobutanedicarboxylic anhydride as a liquid boiling at 151 C.l57 C. under a pressure corresponding to 22 mm. of mercury.

Analysis.Calculated for C H O C, 60.87%; H, 4.38%; M.W., 138.1; sap. eq., 69.06; quant. hydrog, 0.0145 g. of hydrogen/ g. of sample. Found: C, 60.69%; H, 4.48%; M.W., 141; sap. eq., 68.4; C, 61.18%; H, 4.70%; M.W., 157; sap. eq., 68.3; C, 60.81%; H, 4.72%; quant. hydrog., 0.0186 g. of hydrogen/g. of sample.

The infrared spectrum of the product exhibited absorption at 5.4 and 5.6 microns characteristic of the anhydride group and 5.95 and microns characteristic of a terminal methylene group.

Part 2.-A mixture of 37 parts of isobutyl alcohol and 69 parts of the above 3-methylene-1,2-cyclobutanedicar boxylic anhydride was stirred for one hour at C. The resultant yellow liquid solution of the monoisobutyl ester of 3-methylene-1,2-cyclobutanedicarboxylic acid exhibited a neutral equivalent of 202 versus a calculated value of 212. The liquid isobutyl ester was diluted with about 70 parts of absolute methanol, and the resulting solution titrated to neutral using phenolphthalein indicator with a 2.5% solution of lithium hydroxidemonohydrate in absolute methanol (858 g. of the lithium hydroxide solution required). The alcohol was evaporated from the resulting product rapidly by heating on a steam bath with nitrogen blowing over the open vessel. The product was finally dried for three hours at 50 C. under a pres sure corresponding to 3 mm. of mercury. There was thus obtained 106.55 parts (98% conversion) of the lithium salt of the monoisobutyl ester of 3-methylene-1,2-cyclobutanedicarboxylic acid as a yellow, hygroscopic solid.

Analysis.Calculated for C H O Li: Li, 3.2%. Found: Li, 3.4%.

Example B Part ].-A mixture of 138 parts (one molar proportion) of 3-methylenecyclobutane-1,2-dicarboxylic anhydride (see Example A, Part 1) and about 90 parts of acetic anhydride was shaken at 25 C. with a catalytic amount of palladium-on-ch-arcoal hydrogenation catalyst in a pressure-resistant shaker tube of internal capacity corresponding to 500 parts of water and pressured with hydrogen to 1000 lbs/sq. in. gauge. The reaction was exothermic, and as hydrogen was absorbed, the temperature of the reaction mixture increased spontaneously to 85 C. Under these conditions, one molar proportion of hydrogen was absorbed over a period of two hours- The tube was vented and the liquid reaction mixture was; removed. The catalyst was removed by filtration and the acetic anhydride medium removed by distillation. The resultant oil was distilled through a precision fractionation column. There was thus obtained 116 parts (83% of theory) of 3-methylcyclobutane-1,2-dicarboxylic anhydride as a liquid boiling at 153 C. to 152 C. at pressures, respectively, corresponding, to 22 mm. and 21 mm. of mercury; 11 1.4722. The infrared and nuclear magnetic resonance spectra were wholly consistent with the methylcyclobutane dicarboxylic anhydride structure.

In a related experiment, 3-methylenecyclobutane-1,2- dicarboxylic anhydride was hydrogenated at 2 to 3 at- Inospheres of hydrogen pressure over Adams platinum hydrogenation catalyst to afford the 3-methylcyclobutane- 1,2-dicarboxylic anhydride as an oil boiling at 139 (1., under a pressure corresponding to 14 mm. of mercury; 11 1.4743.

Analysis-Calculated for C H O C, 60.0%; H, 5.8%. Found: C, 60.8%; H, 6.1%.

Part 2.A mixture of 56 parts of 3-methyl-1,2-cyclobutane-dicarboxylic anhydride and 52 parts (0.5 molar proportion based on the anhydrides) of 2-ethylhexanol Was heated with stirring under anhydrous conditions at about 120 C. for one hour. The resultant, clear, liquid 2-ethylhexyl ester exhibited a neutral equivalent of 267 versus a theoretical value of 276. The ester was combined with an additional 27 parts made in a similar fashion and theresultant mixture after being diluted with absolute methanol about 1:1 by volume was then titrated to a phenolphthalein end-point with an approximately 2% solution of lithium hydroxide monohydrate in absolute methanol (870.5 parts required). The methanol solvent was removedby evaporation on a steam bath with a nitrogen blanket 'over the surface of the openvessel. The solid product was finally dried by heating at 50 C. under a pressure corresponding to about 3 mm. of mercury. There was thus obtained 118.6 parts of the monolithium salt of the mono-2-ethylhexyl ester of 3-methyl-1,2-cyclobutanedicarboxylic acid as a clear, brittle solid.

Analysis.-Calculated for C H O Li: Li, Found: Li, 2.5%.

The amount of the lithium compound usually employed will vary with the quality and intended use of the fuel. Normally, the amount employed will depend upon the molecular weight of the compound, but should be such as to give 0.01 gram to about 2.0 grams of lithium metal per gallon of the fuel, regardless of. the presence, orthe amount of tetraethyllead in the fuel. Single members of the class of lithium salts of this invention or mixtures of any-two or more members thereof may be used as desired.

Blending agents may be employedtoenhance the solubility of the lithium antiknock compounds of this. invention in the fuel. Typical blending agents are gasoline miscible glycols, esters, ketones, amides, alcohols, and other polar organic liquids. Ethanol, methanol and 'isopropanol are particularly suitable blending agents. The lithium compounds may be dissolved directly in the blended motor fuel or added as a concentrated solution in the blending agent.

In the examples given hereinafter, three knock test methods were employed; the first two beingrepresentative of automotive operating conditions are referred to as the mild test and the severe test, while the third test is representative of supercharged aviation conditions. In the. mild and severe tests, the fuel samples were tested in av Waukesha ASTM D-909-49T knock test method single cylinder, knock rating engine equipped with a four-hole, overhead valve, variable compression ratio head. The engine is mountedon a test stand with a suitable motor-generator unit which absorbs the power output of the engine. A spark plug, mounted in the conventionalposition for this type engine, a rateof change of pressure pick-up and. a steel plug occupy three of the four holes in the head. A Waukesha ASTM90949T knock test method fuel injector is inserted into the fourth hole inthe headby means of an adapter, and is supplied with fuel from the. fuel injection pump. This, fuel system injects the fuel directly into the combustion chamber. With the engine operating, thev occurrence of knock. is determined at the trace knock intensity level by means of therate of change of pressure pick-up mounted in thecylinder head. The signal from the pick-up feeds into a cathode-ray oscilloscope, and the occurrence of knock is observedas a shattering of the rate of change of pressure trace on the oscilloscope screen late in the engine cycle.

The engine is operated under the following conditions:

Test Conditions Oil temperature, F

160 160 Compression ratio Varied to produce trace knock These testsand the test conditions were developed to evaluate antiknock compounds under the same stresses as would be encountered in automotive operation.

Under'these operating conditions, the knock resistance of all fuels-tested is determined by comparing the highest usable knock-free compression ratio of these fuels to that of primary reference fuels consisting of blends of isooctane and n-heptane below 100 performance number, and isooctane plustetraethyllead above 100 performance number. The knock resistance of all fuels tested is. expressed in terms of Army-Navy performance numbers as defined in Tables VII and VIII in the ASTM aviation method (D614-49T), as recorded in the ASTM Manual of Engine Test Methods for Rating Fuels, published by the American Society for. Testing Materials, October 1952.

The supercharged aviation tests were carried out in an engine equipped with manifold fuelv injection in accordance with the procedure set forth in ASTM D-909-49T.

The following examples are given to more clearly illustrate this invention, preferred modes of carrying it into effect and the advantagesous results obtained thereby wherein the percentages employed are by volume except where specifically indicated otherwise.

Example 1 To a blend of hydrocarbons comprising by volume 24% olefines, 60% saturated compounds, and 16% aromatic compounds was added 3 ml. of tetraethyllead per gallon to make a fuel blend having a performance number of 99 in the mild test. To this fuel blend was added lithium methyl adipate to give 0.25 gram of lithiummetal per gallon. As a result, the performance numberof the fuel blend in the mild test was increasedto 107. Asamp'le of the same treated fuel blend gave a. performance number of in the severe test as compared with a performance number of 81.5 obtained with the same fuel but without the lithium methyl adipate.

When methyl lithium and tert.-butyl lithium were tested under mild test conditions, they showed no antiknock. activity. When phenyl lithium was tested under the severetest employing amounts sufficient to provide from 1.06 to 3.18 grams of lithium per gallon of fuel, it increased the performance number of the fuel by only 0.9 to 1.8 units. Lithium oleate, in the above fuel under mild conditions employing 0.25 gram of lithium per gallon of fuel and 5% methanol, but no added tetraethyllead, showed an increase in. the performance number of 1.3; and,-in. the presence of 3 ml. of tetraethyllead per gallon of fuel, showed an increase in performance number of 0 to 5.0. Lithium naphthenate, in the above fuel, had little effect as an antiknock agent, raising the performance. number only 2 units with and without added tetraethyllead, employing 0.25 gram of lithium per gallon of fuel and 5% isopropanol as a solubilizing agent.

Example 2 To portions of a hydrocarbon fuel blend comprising by volume 30% olefinic hydrocarbons, 34% saturated hydrocarbons, and 36% aromatic hydrocarbons and simulating 7 a gasoline stock, was added 3 ml. of tetraethyllead per gallon and a number of lithium salts of monoester dicarboxylic acids. Under the mild test conditions, the performance number of the leaded fuel blend was increased by each of the added lithium salts as shown in the following table:

To portions of isooctane as a base fuel were added lithium isobutyl 3-methylene-1,2-cyclobutanedicarboxylate. The treated fuel with and without added tetraethyllead and isopropanol as a solubilizing agent was then tested for its antiknock rating under the severe supercharged aviation conditions as described in ASTM D-90949T. The increase in the performance number of the fuel provided by the added lithium salt, together with the composition of the fuel, is shown in the following table:

Lithium Isopro- Units Concn TEL, panel, Increase Test g./gal mL/gal Volume in Perfuel fuel Percent formance Number 1 Tetraethyllead.

Lithium oleate, in a proportion to provide 0.25 gram of lithium per gallon of isooctane with 10% ethanol as a solubilizing agent but without added tetraethyllead and tested under the above conditions, increased the performance number only 3.7 units.

Example 4 To an aviation gasoline was added lithium Z-ethylhexyl camphorate to give 0.25 gram of lithium metal per gallon of gasoline and two volume percent of isopropanol as a solubilizing agent. The aviation gasoline was a commercial product consisting mainly of branched chain paraffins in the gasoline boiling range containing 4.5 ml. of tetraethyllead per gallon of fuel and having a performance number of 130 by the ASTM D90949T test. The treated gasoline was then tested for its antiknock rating under supercharged aviation conditions (ASTM D909- 49T) The performance number of the fuel was increased by more than 30 units by the added lithium salt.

It will be understood that the preceding examples have been given for illustrative purposes solely and that this invention is not restricted to the specific embodiments described therein. On the other hand, it will be apparent to those skilled in the art that, subject to the limitations set forth in the general description, the materials, proportions, conditions and techniques employed may be Widely varied without departing from the spirit or scope of this invention. 1

From the preceding description, it will be apparent that this invention provides motor fuels for use in internal combustion engines equipped with fuel injection systems which contain new and improved antiknock compounds that function over the entire range of engine operating conditions and very materially increase the antiknock properties of the fuels. Under severe operating conditions and in the presence of tetraethyllead the new antiknock agents are superior to tetraethyllead. Therefore, it is believed that this invention constitutes a valuable advance in and contribution to the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A motor fuel for internal combustion engines equipped with fuel injection systems which consists essentially of hydrocarbons boiling in the gasoline boiling range containing, in an amount sufiicient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of the formula wherein R is a hydrocarbon radical of 1 to 18 carbon atoms of the group consisting of alkyl and alkenyl radicals and Q is a hydrocarbon radical of l to 10 carbon atoms of the group consisting of saturated acyclic, alicyclic and methylene substituted alicyclic radicals.

2. A motor fuel for internal combustion engines equipped with fuel injection systems which consists essentially of hydrocarbons boiling in the gasoline boiling range which contain, in an amount sufficient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of a monoalkyl ester of an unsubstituted saturated aliphatic dicarboxylic acid of 3 to 12 carbon atoms in which ester the alkyl group contains 1 to 18 carbon atoms.

3. A motor fuel for internal combustion engines equipped with fuel injection systems which consists essentially of hydrocarbons boiling in the gasoline boiling range which contain, in an amount suificient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of a monoalkyl ester of an unsubstituted saturated acyclic dicarboxylic acid of 3 to 12 carbon atoms in which ester the alkyl group contains 1 to 18 carbon atoms.

4. A motor fuel for internal combustion engines equipped with fuel injection systems which consists essentially of hydrocarbons boiling in the gasoline boiling range which contain, in an amount suflicient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of a monoalkenyl ester of an unsubstituted saturated acyclic dicarboxylic acid of 3 to 12 carbon atoms in which ester the alkenyl group contains 2 to 18 carbon atoms.

5. A motor fuel for internal combustion engines equipped with fuel injection systems which consists essentially of hydrocarbons boiling in the gasoline boiling range which contain, in an amount sufiicient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of a monoalkyl ester of tetramethylsuccinic acid in which ester the alkyl group contains 1 to 18 carbon atoms.

6. A motor fuel for internal combustion engines equipped with fuel injection systems which consists essentially of hydrocarbons boiling in the gasoline boiling range which contain, in an amount sufiicient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of a monoalkyl ester of an unsubstituted alicyclic dicarboxylic acid of 3 to 12 carbon atoms in which ester the alkyl group contains 1 to 18 carbon atoms.

7. A motor fuel for internal combustion engines equipped with fuel injection systems which consists es sentially of hydrocarbons boiling in the gasoline boiling range which contain, in an amount sufficient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of a monoalkyl 3,0ss,sia

ester of 3-methyl-1,2-cyclobutane dicarboxylic acid in which ester the alkyl group contains 1 to 18 carbon atoms.

8. A motor fuel for internal combustion engines equipped with fuel injection systems which consists essentially of hydrocarbons boiling in the gasoline boiling range which contain, in an amount sufficient to provide from about 0.01 to about 20 grams of lithium metal per gallon of fuel, lithium ethyl tetramethylsuccinate.

9. A motor fuel for internal combustion engines equipped with fuel injection systems which consists essentially of hydrocarbons boiling in the gasoline boiling range which contain, in an amount sufficient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, lithium Z-ethylhexyl 3-methyl-1,2-cyclobutanedicarboxylate.

10. A motor fuel for internal combustion engines equipped with fuel injection systems which consists essentially of hydrocarbons boiling in the gasoline boiling range containing from about 1.5 to about 6 ml. of tetraethyllead per gallon of fuel and, in an amount sufficient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of the formula wherein R is a hydrocarbon radical of 1 to 18 carbon atoms of the group consisting of alkyl and alkenyl radicals and Q is a hydrocarbon radical of 1 to 10 carbon atoms of the group consisting of saturated acyclic, alicyclic and methylene substituted alicyclic radicals.

11. A motor fuel for internal combustion engines equipped with fuel injection systems which consists essentially of hydrocarbons boiling in the gasoline boiling range which contain from about 1.5 to about 6 ml. of tetraethyllead per gallon of fuel and, in an amount sufficient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of a monoalkyl ester of an unsubstituted saturated aliphatic dicarboxylic acid of 3 to 12 carbon atoms in which ester the alkyl group contains 1 to 18 carbon atoms.

12. A motor fuel for internal combustion engines equipped with fuel injection systems which consists essenitally of hydrocarbons boiling in the gasoline boiling range which contain from about 1.5 to about 6 ml. of tetraethyllead per gallon of fuel and, in an amount sufficient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of a monoalkyl ester of an unsubstituted saturated acyclic dicarboxylic acid of 3 to 12 carbon atoms in which ester the alkyl group contains 1 to 18 carbon atoms.

13. A motor fuel for internal combustion engines equipped with fuel injection systems which consists essentially of hydrocarbons boiling in the gasoline boiling range which contain from about 1.5 to about 6 ml. of tetraethyllead per gallon of fuel and, in an amount suffito provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of a monoalkyl ester of tetramet-hylsuccinic acid in which ester the alkyl group contains 1 to 18 carbon atoms.

14. A motor fuel for internal combustion engines equipped with fuel injection systems which consists essentially of hydrocarbons boiling in the gasoline boiling range which contain from about 1.5 to about 6 ml. of tetraethyllea-d per gallon of fuel and, in an amount sufficient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of a monoalkyl ester of an unsubstituted alicyclic dicarboXylic acid of 3 to 12 carbon atoms in which ester the alkyl group contains 1 to 18 carbon atoms.

15. A motor fuel for internal combustion engines equipped with fuel injection systems which consists essentially of hydrocarbons boiling in the gasoline boiling range which contain from about 1.5 to about 6 ml. of tetraethyllead per gallon of fuel and, in an amount sufficient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, lithium ethyl tetramethylsuccinate.

16. A motor fuel for internal combustion engines equipped with fuel injection systems which consists essentially of hydrocarbons boiling in the gasoline boiling range which contain from about 1.5 to about 6 ml. of tetraethyllead per gallon of fuel and, in an amount sufficient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, lithium Z-ethylhexyl 3-methyl-1,2 cyclobutanedicarboxylate.

References Cited in the file of this patent UNITED STATES PATENTS 1 2,460,700 Lyons Feb. 1, 1949 2,728,648 Hirschler et al Dec. 27, 1955 2,834,662 Hirschler et al. May 13, 1958 2,834,663 Hinkamp et al. May 13, 1958 2,834,664 Irish et al. May 13, 1958 2,935,973 Sandy et al. May 10, 1960 2,935,974 Sandy et al May 10, 1960 2,935,975 Sandy et al May 10, 1960 FOREIGN PATENTS 300,156 Great Britain Nov. 6, 1928 837,965 France Nov. 28, 1938 

1. A MOTOR FUEL FOR INTERNAL COMBUSTION ENGINES EQUIPPED WITH FUEL INJECTION SYSTEM WHICH CONSISTS ESSENTIALLY OF HYDROCARBONS BOILING IN THE GASOLINE BOILING RANGE CONTAINING, IN AN AMOUNT SUFFICIENT TO PROVIDE FROM ABOUT 0.01 TO ABOUT 2.0 GRAMS OF LITHIUM METAL PER GALLON OF FUEL, AT LEAST ONE LITHIUM SALT OF THE FORMULA 